Heated window

ABSTRACT

A heated window including at least one rigid pane, at least two current busbars of different polarity placed substantially parallel close to one edge of the heated window at different distances from the edge, and linear heating resistors electrically connected thereto. The busbars lie sideways to the heating resistors and the heating resistors start from a first current busbar and, passing over the other current busbar while being insulated therefrom, in the direction of the window surface and in at least one loop, return toward the other current busbar and are electrically connected thereto.

The invention relates to a heated window consisting of at least onerigid pane, at least two current busbars of different polarity placedsubstantially parallel close to one edge of the heated window atdifferent distances from the edge, and linear heating resistorselectrically connected thereto.

These features are known from German utility model DE 296 06 071 U1,which relates to a laminated window with electric heating, in whichheating resistors are provided electrically mounted in parallel andembedded in the intermediate thermoplastic layer in the region of therest position of the windshield wipers. Also, metal film strips actingas busbars connected to electrical power supply lines, and which areelectrically connected to the heating resistors, are embedded in theintermediate thermoplastic layer. The busbars are arranged very close toeach other and the heating resistors are placed, in the form of loops,between the busbars. In one embodiment, the heating resistors arearranged as U-shaped loops, one interleaved with the other in thehorizontal direction and brazed to two ribbon-shaped current busbars.The current busbars are very close and parallel to each other in theregion of one side edge of the windshield. The current busbar away fromthe edge of the windshield is only about half as long as the currentbusbar placed in the immediate proximity of the side edge, this currentbusbar being connected to the upper halves of the wire loops, and theother current busbar being connected to the lower halves of the wireloops.

A windshield with electric heating provided with a flat heater, with twocurrent busbars placed at the opposite upper and lower edges of thewindow is known from EP 0 479 154 A1. The lower current busbar isprovided in the middle with a current lead oriented perpendicularly tothe edge of the window, therefore in the shape of a T. The upper currentbusbar is connected to two leads, which are placed along the two sideedges. The two leads further extend along the lower edge of the windowbelow the lower current busbar. The first lead transversely crosses,under electrical insulation, the perpendicular branch of the T and iselectrically connected to the other lead. The other lead is also takentoward the lower edge of the window. Because of this arrangement, onlytwo electrical connection lines are needed in the middle of the loweredge of the windshield.

The object of the invention is to produce another heated window withcurrent busbars arranged close to one edge of the window.

According to the invention, this objective is achieved by the fact thatthe busbars lie sideways to the heating resistors and the heatingresistors start from a first current busbar and, passing over the othercurrent busbar while being insulated therefrom, in the direction of thewindow surface and in at least one loop, return toward the other currentbusbar and are electrically connected thereto. The characteristics ofthe secondary claims reveal the advantageous improvements of thisobject.

According to the invention, the heating resistors extend from onecurrent busbar away from the edge in the direction of the face to beheated and they return back in a loop toward another current busbarclose to the edge, crossing the current busbar away from the edge. Thecurrent busbars close to and away from the edge are arranged in theregion of the same edge of the window. To prevent a short circuit, theheating resistor is electrically insulated from the current busbar inthe region of the crossing. The heating resistors thus arranged form aheating field, which lies over a particular zone of the heated windowand which is supplied with electrical energy by the pair of currentbusbars.

The invention is not limited to the fact that there is only a singleheating field on the heated window. It may, for example, be beneficialto provide several heating fields, especially to produce differentheating powers in particular zones. It is thus possible to imaginearranging two or more than two heating fields side by side in the faceof the window. The respective pairs of current busbars, for example, fortwo heating fields, may be at the same edge of the window, the currentleads coming from the upper edge for a first upper heating field, andfrom the lower edge for the other lower heating field. If the currentlead must be effected from a single edge of the window, it is necessaryto cross, in an insulated manner, more than one current busbar. Inanother variant, it is possible to use one current busbar as a commonground terminal for the two heating fields. Furthermore, it is possibleto arrange the pairs of busbars for different heating fields atdifferent side edges. The heating fields then cover zones of the heatedwindow, which are arranged at a distance from each other, are contiguousor even are interleaved with each other.

In another variant of the heated window, the heating resistors formseveral loops, before returning to the other current busbar. The heatingresistors therefore do not extend only from the busbar away from theedge over the width of the heating field to return again toward thebusbar close to the edge, but they go back into at least another loopagain over the width of the heating field toward the pair of busbars.Therefore there is always an odd number of conducting loops. For aspecific heating resistor, which depends on the length of the conductor,on the cross section of the conductor and on the specific resistance ofthe material used, it is possible to adjust the heating power per unitarea by choosing the number of loops, independently of the geometricaldimensions of the surface to be heated. The use of a greater number ofloops has the additional advantage that the number of electricalconnections, which in general must be produced by brazing, is smallerthan when arranging the heating resistors in a single loop each time. Itis thus possible to save on the number of working steps.

The heated windows according to the invention may be monolithic windows,in which the heating resistors are placed on one of their main faces. Aknown example of this type of window is supplied by motor vehiclewindows or by toughened safety-glass windows, which are provided withheating resistors made of a conducting matrix. Normally, a conductingceramic paste with a high silver content is screen printed in the shapedesired for the heating conductors and the conducting busbars on thesurface of the window for this purpose, and it is then baked. Theconducting busbar away from the edge can be insulated from the conductorwhich crosses it by means of a dielectric matrix. For this purpose, theprinting operation for the heating resistors and the busbars must besplit into two steps. In a first step, the current busbar away from theedge is printed with the heating resistors, and the return branch of theloop of the heating conductor terminates slightly before the currentbusbar away from the edge. The second step follows, in which aninsulating layer, for example a dielectric matrix to be baked, isarranged on this current busbar. Next, the current busbar close to theedge is printed, and the connecting conductors are placed at the sametime toward the open ends of the loops of the heating conductors. Theconnecting conductors cross, in an insulated manner, the busbar awayfrom the edge and close the electric circuit of each individual heatingresistor loop.

A series of printed conducting and insulating layers is known fromGerman patent DE 39 11 178 C2. In this case, an output antenna conductoris made in the form of a coaxial pseudoconductor with powerfulshielding.

Apart from monolithic heated windows, the invention also comprisesheated windows made of laminated glass, which consist of at least tworigid panes assembled to each other by adhesive bonding by means of anintermediate layer. In this case, the heating resistors are preferablycomposed of metal wires, which are embedded in the intermediate layer.However, it is also possible to manufacture a heated laminated windowaccording to the invention by using the monolithic heated windowdescribed in order to form one of the individual panes. The surface withthe heating resistors may just as well be placed on the inside as on theoutside of the laminated glass. The individual panes may consist ofglass or of plastic. The laminated windows may be composed of two ormore panes of identical or different materials. Normally, an adhesivethermoplastic film, for example made of polyvinyl butyral, is used as anintermediate layer assembling the individual panes to each other.

The current busbars in the laminated windows, which may be heated bymeans of heating resistors embedded in the intermediate layer, normallyconsist of flat metal films made of tinned copper. There are also modelswhich are further provided with an insulating coating made of polyimide.With a metal film strip of this sort acting as a current busbar awayfrom the edge, a laminated window according to the invention may beeasily manufactured by removing the insulator only at the locationswhere the heating resistors must be electrically connected to thecurrent busbar. The current busbar close to the edge may be placedwithout an insulating coating or, where an insulated metal film strip isused, the insulator may also be removed at its locations of connectionwith the heating resistors.

To ensure that vision through the laminated window is hindered as littleas possible, the heating wires must have a relatively small diameter ofabout 20 μm to 100 μm. Heating wires made of tungsten have proved to besuitable for this purpose. However, copper wires, which can be providedwith a layer of a dark matt color in order to prevent metallicreflections, are also suitable to be used in the laminated windowaccording to the invention. Wires with several layers are also known,which have a mechanically strong core which is enveloped by a metalwhich is a good conductor and/or easy to braze. The material for thewires and/or the diameter of the wires is chosen according to mechanicaland electrical requirements associated with the desired heating field.

When the wires are straight and arranged in parallel at a short distancefrom each other, phenomena of diffraction on incidence of the light mayoccur under unfavorable circumstances. Such phenomena can be preventedby certain irregularities in the alignment of the heating wires, forexample a wavy arrangement of the heating wires.

When the current busbars are only arranged close to a single side edge,the laminated window is suitable, for example, for use as a heatedlaminated window with free edges, therefore for example as a motorvehicle side window which can be opened. The current busbars can bearranged inside the well of the door and be masked by the bodywork orsealing elements.

Other details and advantages of the subject of the invention willemerge, without any intention of limitation, from the drawing of oneembodiment and from its detailed description which follows.

In the drawings, which constitute a simplified representation without aparticular scale,

FIG. 1 shows a laminated window according to the invention as a sidewindow of a motor vehicle, in elevation; and

FIG. 2 shows a section through the side window of FIG. 1 along the lineI—I.

According to FIG. 1, a laminated window 1 is provided with heating wires2 made of black lacquered copper, which are placed inside the laminatedwindow 1 and whose diameter is about 85 μm. The heating wires 2 lie inthe shape of a loop between the lower edge of the side window 1 in thefitted position and its upper edge. In order to supply it withelectricity, a first end of each loop is connected to a current busbar 3and the other end of the loop is connected to the current busbar 4. Onthe path toward the current busbar 4, the heating wires 2 must cross thecurrent busbar 3 in the zones 31. In these zones 31, the heating wires 2are electrically insulated from the current busbar 3. The two currentbusbars 3 and 4 are, like the heating wires 2, placed inside thelaminated window 1 and are connected to the two poles of an on-boardelectrical network. Normally, there is a voltage of 12 V between thecurrent busbars. The current supplied complies with the heating powerneeded per unit area, for which it is necessary to take into account theelectrical resistance of the heating wires 2 and their mutualseparation. In order to distribute the heating power constantly over theface of the laminated window 1, the length of the wires of theindividual loops must also be as equal as possible, the other propertiesof the wires being equal. Consequently, for the laminated window shownin FIG. 1, the portion of wire which is in the region of the inclinededge and therefore of lower height has been arranged in a loop with fivechanges of direction, while each of the other portions of wire changedirection only three times.

The current busbars 3 and 4 leave the laminated window 1 at the side andare connected in a known manner to the on-board network. For the carside window shown here, the part next to the lower edge of the window,in which the current busbars are located, is arranged inside the doorwell and is thus masked by the bodywork. Moreover, the normal masking ofthe current busbars using layers of an opaque color is not necessary inthis case.

FIG. 2 shows a representation in section of the side window of FIG. 1along the line I—I. The laminated window 1 is composed of two individualpanes 11 and 12 with a thickness of about 2.1 mm, which are assembled toeach other in a known manner by adhesive bonding with insertion of anintermediate thermoplastic layer 13 made of polyvinyl butyral. Beforethe assembly operation, the heating wires 2 and the current busbars 3and 4 are embedded in the surface of the intermediate layer 13 using amethod which is also known.

The current busbar 4 is composed of a tinned copper film and ismechanically and electrically connected to the heating wire 2 bybrazing. In contrast, for the current busbar 3, a tinned copper film 32is surrounded on all sides by an insulating coating 33 made ofpolyimide. The heating wire 2 can therefore cross the current busbar 3,where it will certainly touch it but nevertheless will have noelectrical contact therewith. At the locations where the heating wire 2is electrically connected to the current busbar 3, the insulatingcoating must be removed before encapsulation in the intermediatethermoplastic layer.

1. A heated window comprising: at least one rigid pane; at least twocurrent busbars of different polarities placed substantially parallelclose to one edge of the heated window at different distances from theedge; and at least two heating resistors having looped shapeselectrically connected to the busbars, wherein the busbars lie sidewaysto the heating resistors and a first end of a first heating resistor iselectrically connected to a first current busbar, the first heatingresistor extends in a direction of the window surface and in at leastone loop, returns toward a second current busbar and is electricallyconnected to the second current busbar, and a second end of the firstheating resistor crosses the first busbar at an insulated portion andconnects to the second bus bar.
 2. The heated window as claimed in claim1, wherein the heating resistors return toward the second current busbarafter having formed more than one loop and are electrically connected tothe second current busbar.
 3. The heated window as claimed in claim 1,wherein the rigid pane comprises a glass pane and the heating resistorscomprise a baked conducting ceramic matrix.
 4. The heated window asclaimed in claim 1, wherein the at least one rigid pane comprises alaminated window including at least two rigid panes assembled to eachother by adhesive bonding by an intermediate layer.
 5. The heated windowas claimed in claim 4, wherein the heating resistors are embedded in theintermediate layer and the current busbars comprise strips of metalfilm.
 6. The heated window as claimed in claim 5, wherein at least onemetal film strip is surrounded with an insulating sheath, which is onlybroken in a region of the electrical connection with a heating resistor.7. The heated window as claimed in claim 5, wherein the heatingresistors comprise tungsten wire.
 8. The heated window as claimed inclaim 5, wherein the heating resistors comprise copper wire.
 9. Theheated window as claimed in claim 5, wherein the heating resistorscomprise plural conducting materials, of a first mechanically strongmetal and a second metal having a higher electrical conductivity. 10.The heated window as claimed in claim 5, wherein the heating resistorsare embedded in the intermediate layer in a wavy arrangement.
 11. Theheated window as claimed in claim 5, wherein the heating resistors areembedded in the intermediate layer in a straight arrangement.
 12. Theheated window as claimed in claim 5, wherein at least one of the panescomprises glass.
 13. The heated window as claimed in 5, wherein theintermediate layer comprises a thermoplastic polymer.
 14. The heatedwindow as claimed in 1, wherein the heated window comprises a motorvehicle side window that can be opened and the current busbars arearranged in a masked position.
 15. The heated window as claimed in claim13, wherein the thermoplastic polymer comprises polyvinyl butyral.